1. Field of the Invention
The invention relates generally to adhesive dispersing systems and more particularly to processes and apparatus for bonding one or more relatively elongated strands to one or more substances, especially bonding stretched elastic strands to fabrics in the manufacture of absorbent garments.
2. Description of Related Art
Disposable absorbent garments such as infant diapers or training pants, adult incontinence products, and other such products are well-known in the art. Typically, the chassis of such garments comprises a liquid-permeable body-contacting liner sheet (or xe2x80x9ctopsheetxe2x80x9d), a liquid-impermeable backing sheet (or xe2x80x9cbacksheetxe2x80x9d) (collectively the xe2x80x9csheetsxe2x80x9d), and a moisture-absorbent core fiber (or xe2x80x9cabsorbent corexe2x80x9d) that usually is made of a non-woven mat of randomly arranged fiber and is generally disposed between the topsheet and the backsheet.
These absorbent garments often times incorporate elastic elements in the waist, tummy and leg areas for improving the fit of the garment. The waist and tummy elastic elements increase the flexibility of the garment, allowing the same garment to accommodate a greater range of body sizes. In addition, they make the garment more form-fitting for the wearer. Leg gather elastic elements and standing leg gathers have also been employed to help reduce leakage of bodily exudates from the garment when the absorbent core cannot absorb body exudates fast enough. Leg gathers are known in the art, and U.S. Pat. No. 5,660,664 issued to Herman (the xe2x80x9c""664 Patentxe2x80x9d) discloses an exemplary method of manufacturing leg gathers, the disclosure of which is incorporated by reference herein in its entirety.
These garments typically are prepared by continuously supplying the various components of the garment, and forming these components into the final garment. The elastic elements are continuously supplied at several different points of the assembly process, they typically are extended and then adhered to the garment components.
Typically the adhesive is sprayed onto stretched elastic strands disposed on or very near an underlying fabric substrate moving relative to one or more adhesive dispensing nozzles. The adhesive usually is a hot melt adhesive that is applied generously to both the substrate and the elastic strands simultaneously. Application of generous amounts of adhesive to substrate is often the result of inefficiency of application methods and does not typically provide bonding benefits. The stretched elastic strand is usually bonded between overlapping fabric layers. As the stretched elastic strands contracts, the fabric adhered thereto is bunched together forming generally pleated waist bands and other stretchable portions of the undergarment. It is important that the elastic strand be bonded to the fabric substantially continuously along its axial length to be bonded to ensure uniform pleating, or bunching, of the fabric, which is necessary for optimum comfort and fluid absorption, and to provide an aesthetically pleasing product.
Methods of bonding elastics to garment materials have been previously discussed in the art. An example of disposing elastic elements between layers of sheet material is provided in U.S. Pat. No. 5,870,778 issued to Tharpe, the disclosure of which is incorporated by reference herein in its entirety. Tharpe discloses coating the garment materials with adhesive to affix the elastic elements therein. A common procedure for affixing elastic elements in the industry today is a spiral spray adhesive application as disclosed in U.S. Pat. No. 4,815,660, issued to Boger, the disclosure of which is incorporated by reference herein in its entirety. Spiral spray adhesive application consists of ejecting a bead of hot melt adhesive, directing jets of pressurized air to form an elongated adhesive fiber from the bead, and imparting a rotational motion to the adhesive fiber. The spirals of adhesive are then deposited on the target substrate, typically a non-woven material. In usage, the adhesive spray coats not only the elastic elements but also xe2x80x9coverspraysxe2x80x9d to other sites, causing a number of undesirable consequences.
Some of these disadvantages include: The garment materials that are xe2x80x9coversprayed,xe2x80x9d e.g., portions of the topsheet, the bottom sheet, and the absorbent core, become rigid upon hardening of the xe2x80x9coversprayedxe2x80x9d adhesive making the garment less comfortable for its wearer. This has been referred to as the xe2x80x9cplywood effect.xe2x80x9d The xe2x80x9coversprayxe2x80x9d also may coat parts of the assembly machinery that must then be periodically cleaned of the adhesive. The elastic elements and/or the substrates to which they are to adhere may not be uniformly coated with the adhesive due to the nature of the spraying operation, and therefore the elastic elements may not bond to the garment materials as well as if they had been more uniformly and completely coated with the adhesive. Finally, the xe2x80x9coversprayxe2x80x9d is wasted adhesive, increasing the cost of materials for the finished garment.
Attempts have been made to reduce the amount of excess adhesive that is applied to the garment. U.S. Pat. No. 5,993,433 issued to St. Louis et al., which is incorporated herein by reference in its entirety, discloses an adhesive pattern for applying adhesives to the gathers, but such adhesive patterns still contribute to excessive garment stiffness and cost. U.S. Pat. No. 6,235,137 B1 issued to Van Eperen et al., which is incorporated herein by reference in its entirety, discloses a method of coating an elastic strand with a filament of adhesive, but this coating process is still subject to overspraying, and does not provide a complete coating of adhesive on the elastic.
In addition to stiffness and cost concerns, applying excess adhesive onto the elastic strands and underlying substrate than is required for bonding may, in the case of the typically used hot melt adhesives, have a tendency to deform the relatively thin, temperature sensitive fabric, thereby providing an undesirable appearance. In extreme cases the hot adhesive may destroy the fabric by burning a hole through the fabric.
Further excess adhesive applied onto the fabric may reduce the fluid absorbing capacity of the fabric and possibly result in the leakage of bodily fluids from the absorbent garment. Additionally, the adhesive stiffened fabric may be slightly abrasive against the skin, and in some extreme cases may irritate sensitive skin.
U.S. Pat. No. 5,507,909 to Rollins et al., (the xe2x80x9cRollins ""909 Patentxe2x80x9d) discloses a process and apparatus for helically wrapping adhesive onto an elastic strand, which is bonded to a substrate in the manufacture of disposable absorbent products. The disclosure of the Rollins ""909 patent is incorporated by reference herein in its entirety. To helically coat the elastic strand with adhesive, the strand is rotated about its axis as it is drawn past an adhesive flow from a dispensing orifice, for example by drawing the elastic strand between a nip roll assembly rotated at an angle relative thereto.
The process and apparatus disclosed in the Rollins ""909 Patent allegedly reduces the amount of adhesive applied to the substrate and applies more conservative amounts of adhesive onto the elastic strand, but the uniform application of adhesive helically about the strand requires consistently and uniformly controlling the rotation of the strand during the drawing thereof. If the adhesive is not applied uniformly along the axial dimension of the strand, the stretched strand may not bond uniformly to the substrate, which adversely affects uniform bunching of the fabric. Non-uniform bunching is undesirable from an aesthetic viewpoint, and more substantively non-uniform bunching of the fabric compromises the ability of the fabric to form an effective fluid seal, and reduces the softness and comfort thereof when stretched against the wearer""s body.
U.S. Pat. No. 6,077,375 to Kwok (the xe2x80x9cKwok ""375 Patentxe2x80x9d) discloses applying fluids including adhesives onto strands. More particularly the Kwok ""375 Patent discloses methods for applying fluids to a strand, useable for bonding the strand to a substrate in the production of bodily fluid absorbing hygienic articles, by drawing the strand along an isolated path, moving a fluid fiber across a path of the strand as the fluid fiber is dispensed toward the strand so that the fiber contacts the strand, and substantially all of the fiber is captured on the isolated strand. The disclosure of the Kwok ""375 Patent is incorporated by reference herein in its entirety. The fiber is oscillated back and forth across a path of the strand, and beyond opposing sides thereof to at least partially coat all sides thereof with fluid.
In an exemplary application of the method disclosed in the Kwok ""375 Patent, the fluid fiber is a substantially continuous hot melt adhesive fiber dispensed from an adhesive orifice. The adhesive fiber oscillates back and forth across the path of an elastic strand and beyond opposing sides thereof under the influence of first and second air flows dispensed from first and second air orifices disposed on opposing sides of a corresponding adhesive orifice.
The amplitude and frequency of oscillation of adhesive fibers is controlled by the first and second air flows. In an alternative embodiment, the ""375 Patent describes dispensing hot melt adhesive fibers from a spiral nozzle in a swirling pattern to move the adhesive fiber back and forth across the path of the strand as the adhesive fiber is dispensed toward the strand. The use of air jets near the adhesive dispensing nozzle as described in the ""375 Patent may lead to clogging of the adhesive dispensing nozzle or dispense adhesive fumes in the manufacturing environment or both.
The foregoing description of the various products, methods, and apparatus, and their attendant disadvantages is in no way intended to limit the scope of the present invention, or to imply that the present invention does not include some or all of the various elements of the products, methods, and apparatus in one form or another. Indeed, various embodiments of the invention may be capable of overcoming some of the disadvantages, while still retaining some or all of the various elements of the products, methods, and apparatus in one form or another.
There exists a need to manufacture a softer absorbent garment that has not had materials xe2x80x9coversprayedxe2x80x9d with adhesive during coating of the elastic elements for assembly. A need also exists for a clean, more efficient, cost effective method of applying adhesive to the elastic elements for assembly into an absorbent garment. Additionally, a need exists to more uniformly and completely coat elastic elements with adhesive prior to bonding to an absorbent garment to promote product uniformity and improved adhesion of the elastic elements to the garment. Further, a need exists to reduce the use of air jets near adhesive application nozzles to improve maintenance requirements, and to improve environmental aspects of the manufacturing area.
It therefore is a feature of various embodiments of the invention to address the aforementioned needs by providing a method for discretely coating elastic strands with fluid adhesive fibers prior to incorporation of the elastic strands into absorbent garments. In accordance with these and other features of the invention, there is provided a method for applying a fiberized fluid adhesive to a strand that comprises: supplying a strand along a machine direction; dispensing a substantially continuous fluid adhesive fiber toward the strand in a direction normal to the machine direction; oscillating the strand back and forth in a direction orthogonal to the machine direction, and in a plane normal to the continuous fluid adhesive fiber across the path of the fluid adhesive fiber as the fluid adhesive fiber is dispensed toward the strand; capturing substantially all of the continuous fluid adhesive fiber on the strand; and coating all sides of the strand at least partially with the fluid adhesive fiber. In one exemplary embodiment, dispensing the continuous fluid adhesive fiber is initiated and terminated at predetermined intervals.
In accordance with another embodiment of the invention, there is provided a method of bonding a strand to a substrate comprising: drawing the strand along a path separated spatially from a first substrate; dispensing the fluid adhesive fiber from above the strand; capturing substantially all of the fluid adhesive fiber on the strand when the strand is spatially separated from the first substrate; coating all sides of the strand at least partially with the adhesive fiber when the strand is spatially separated from the first substrate; and contacting the adhesive coated strand with the substrate to bond the strand to the first substrate. A method of making a laminate also is disclosed whereby during or after the adhesive coated strand is bonded to the first substrate, a second substrate is provided so that the adhesive coated strand is disposed between the first and second substrates.
In another exemplary embodiment of the invention, the method may comprise supplying a plurality of strands separated spatially from a substrate and from each other in a machine direction, dispensing a plurality of adhesive fibers from a corresponding plurality of adhesive orifices toward a corresponding one of the plurality of strands; oscillating each of the plurality of strands back and forth in a direction orthogonal to the machine direction, and in a plane normal to the continuous fluid adhesive fiber across the path of the corresponding adhesive fibers as the fluid adhesive fibers are dispensed toward the strands, capturing substantially all of each adhesive fiber on the corresponding strand when the strand is substantially separated from the substrate, at least partially coating all sides of each strand with the corresponding adhesive fiber when the strand is spatially separated from the substrate; and contacting the plurality of adhesive coated strands with the substrate to bond the plurality of strands to the substrate.
In one preferred embodiment the method described above is used for applying adhesive to a strand for bonding the strand to a substrate in the manufacture of an absorbent garment. In another preferred embodiment, the strand is a strand of elastic material.
The invention further includes an apparatus for applying fluid filaments to a strand, a method and apparatus for making a laminate including two outer layers having a strand disposed there between, and a method and apparatus for forming an absorbent garment. The apparatus for applying fluid filaments to a strand comprises: a dispensing nozzle for dispensing fluid filaments to a strand; a strand supply mechanism for supplying a strand in a machine direction that is substantially normal to the path of the fluid filament dispensed from the dispensing nozzle; and a mechanism for oscillating the strand in a direction orthogonal to the machine direction, and in a plane substantially orthogonal to the path of the fluid filament.
The apparatus for making a laminate comprises, in addition to the apparatus described above for applying fluid filaments to a strand, a first substrate supply mechanism for supplying a first substrate in the machine direction, whereby the strand is positioned between the dispensing nozzle and the first substrate. The apparatus further includes a second substrate supply mechanism for supplying a second substrate such that the strand is disposed between the first substrate and the second substrate, and a mechanism for bringing the first substrate, strand, and second substrate together to form a laminate.
In accordance with another feature of an embodiment of the invention, there is provided a method of making an absorbent garment that includes providing a top sheet material, a back sheet material, and an absorbent core. The method also includes applying a fluid filament to a strand in accordance with the method described above, and disposing fluid filament-coated strand and the absorbent core between the top sheet material and the back sheet material.
In accordance with another feature of an embodiment of the invention, there is provided a method of making an absorbent garment that includes providing a top sheet material, a back sheet material, and an absorbent core, and disposing the absorbent core between the top sheet material and the back sheet material to form an absorbent core assembly. The method also includes making a laminate that includes a first substrate, a second substrate, and a strand disposed between the first and second substrates in accordance with the method described above. The method also includes attaching the laminate to the absorbent core assembly.
In accordance with another feature of an embodiment of the invention, there is provided an apparatus for forming an absorbent garment that includes a top sheet supply mechanism, a back sheet supply mechanism, and an absorbent core supply mechanism for supplying each of the respective components to a forming station. The apparatus further includes either the apparatus for applying a fluid filament to a strand or the apparatus for making a laminate as described above, or both. The apparatus includes further a forming station for disposing the absorbent core and fluid filament-coated strand between the top sheet material and the back sheet material. The forming station may also optionally have a laminated attachment station that is capable of attaching the optional laminate to either the backsheet material, the top sheet material, or both.